1. Field of the Invention
The present invention relates to, for example, a transistor or a semiconductor device. The present invention relates to, for example, a method for manufacturing a transistor or a semiconductor device. The present invention relates to, for example, a display device, a light-emitting device, a lighting device, a power storage device, a memory device, a processor, and an electronic device. The present invention relates to a method for manufacturing a display device, a liquid crystal display device, a light-emitting device, a memory device, or an electronic device. The present invention relates to a method for driving a display device, a liquid crystal display device, a light-emitting device, a memory device, or an electronic device.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. Furthermore, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, a light-emitting device, a lighting device, an electro-optical device, a semiconductor circuit, and an electronic device include a semiconductor device in some cases.
2. Description of the Related Art
Transistors formed using silicon are widely used in various integrated circuits (IC) such as a CPU and a memory included in electronic devices. The integration of integrated circuits and miniaturization of transistors have progressed in accordance with an increase in performance and a reduction in size and weight of electronic devices. Thus, the process rule for fabricating a transistor has decreased year by year as follows: 45 nm, 32 nm, and 22 nm.
The miniaturization of transistors causes a problem called a short-channel effect. The short-channel effect refers to degradation of electric characteristics which becomes obvious with miniaturization of a transistor (a reduction in channel length (gate length)) and arises by the influence of an electric field from a drain electrode on a source electrode. Specific examples of the short-channel effect include a decrease in threshold voltage, an increase in subthreshold swing, an increase in leakage current, and the like.
As a countermeasure against the short-channel effect, a nanowire transistor has been proposed (see Patent Document 1). A nanowire transistor is a transistor that uses extremely narrow cylindrical silicon with a diameter of several nanometers to several tens of nanometers in its active layer. In the nanowire transistor, a gate surrounds the silicon in the direction crossing the extending direction of the silicon; the gate electrode all around the silicon can prevent the influence of an electric field from the drain electrode on the source electrode.